Process for the bulk polymerization of acrylonitrile

ABSTRACT

FREE-RADICAL BULK POLYMERIZATION OF ACRYLONITRILE WITH OR WITHOUT ANOTHER COPOLYMERIZABLE ETHYLENICALLY UNSATURATED MONOMER, USING A FREE-RADICAL CATALYTIC SYSTEM HAVING A DECOMPOSITION RATE CONSTANT (KD) GREATER THAN 1 HR.-1 AT THE POLYMERIZATION TEMPERATURE, A REACTION TIME (Q) SUFFICIENT TO SEMI-DECOMPOSE THE CATALYST, AND A CATALYST CONCENTRATION (C) EQUAL TO OR GREATER THAN 2.10-3 Q MOLES LITER, WHEREIN &#34;Q&#34; IS THE RESIDENCE TIME EXPRESSED IN HOURS.

United States Patent US. Cl. 260-63 N 8 Claims ABSTRACT OF THE DISCLOSURE Free-radical bulk polymerization of acrylonitrile with or without another copolymerizable ethylenically unsaturated monomer, using a free-radical catalytic system having a decomposition rate constant (K greater than 1 hr.- at the polymerization temperature, a reaction time (Q) sutlicient to semi-decompose the catalyst, and a catalyst concentration (C) equal to or greater than 2.1() Q moles/liter, wherein Q is the residence time expressed in hours.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a process for the bulk polymerization of acrylonitrile. More particularly, the present invention concerns an improved process for freeradical bulk polymerization of acrylonitrile which process provides a high degree of control of the reaction conditions and the reaction mixture vicosity and results in high polymerization conversions.

(2) Description of the prior art Heretofore the free-radical bulk polymerization of acrylonitrile at room temperature or higher temperatures has not been an industrially feasible process.

Primarily, this has been due to the difliculty of 1) finding a catalytic system soluble in the monomer, and capable of achieving a high degree of efliciency together with an easy control of the polymerization reaction, and (2) of finding reaction conditions suitable to maintain the polymerization mixture in a sufiiciently fluid state to facilitate mixing the reaction medium and dispersion of the heat generated by the reaction.

Thus, it is well known that the bulk polymerization of acrylonitrile, under certain conditions, can become autocatalytic, which can lead to loss of control of the polymerization and explosions due to the rapid development of hot spots. The self-catalytic course of this type of reaction is due to the reduction of the chain-termination rate of the macroradicals resulting from their being trapped in the precipitated polymer. (See W. H. Thomas in Mechanism of Acrylontrile Polymerization Fortschritte der Hochpolymeren-Forschung, 2nd volume, pages 401-411, 1961.)

The extent of this phenomenon, referred to in the literature as the gel effect, depends on the degree of swelling of the polymer in the reaction medium and, thus, on its apparent density. Inasmuch as, during the polymerization, the polymerization medium rapidly thickens due to the adsorption of the monomer into the polymer, it becomes increasingly difiEicult to stir the mixture and dissipate the heat of the reaction. Consequently, the increase of polymerization rate, combined with the contemporaneous increase in viscosity of the polymerization medium, causes the temperature to rise, which in turn further increases the reaction rate. Thus, the polymeriza-' tion gradually gets out of control and often results in an explosion.

It is known that this catalytic effect of the precipitated polymer on the polymerization rate increases proportionally with the concentration of the catalyst. (See C. H. Bamford, W. G. Barb, A. D. Jenkins, and P. F. Onyon- The Kinetics of Vinyl Polymerization by Radical Mechanism-Butterworts 1958, page 113.)

Kinetically expressed, the polymerization rate (R11) is dependent on the concentration (C) of the catalyst according to the equation:

wherein, K is a constant, while a ranges from 0.7 to 0.9, instead of being equal to 0.5 as in the case of non self catalytic polymerizations. (See C. H. Bamford, W. G. Barb, A. D. Jenkins, and P. F. Onylonsupra, and C. H. Bamford, and A. D. Jenkins, Proc. Roy. Soc., London, Ser. A. 216,515, 1953).

In the bulk polymerization of acrylonitrile catalyzed by benzoyl peroxide or azo-bis-iso-butyronitrile, values for a of 0.75 and 0.82, respectively, have been observed. (See W. M. Thomas, I. Polymer Sci., No. 13, page 329, 1954.) These values indicate the self-catalytic nature of the polymerization reaction.

To date, the industrial scale bulk polymerization of acrylonitrile has been considered unfesible because the process could be controlled only at low initiation rates and with small quantities of reaction monomer. (See W. H. Thomas, Mechanism of Acrylonitrile Polymerization"-Fortschritte der Hochpolymeren-Forschung, volume 2, page 410, 1961.)

As is evident from the foregoing, the temperature of such processes must be controlled by the continuous removal of the polymerization heat. For this purpose it is necessary, especially when large reactors are used, to maintain the viscosity of the polymerization medium at low levels. That is to say, it is necessary to operate under such conditions as to minimize the amount of monomer absorbed by the polymer.

Although it is recognized that in order to minimize the monomer adsorption the polymer must possess a compact structure, generally accompanied by a high apparent density, methods for accomplishing this, particularly on an industrial scale, have not been available.

SUMMARY OF THE INVENTION We have discovered a new process for the free-radical catalyzed, bulk polymerization of acrylonitrile, with or without another copolymerizable ethylenically unsaturated monomer, wherein the polymer exhibits a high apparent density, thereby permitting excellent and facile control of the polymerization temperature. Our invention comprises carrying out the bulk polymerization of the acrylonitrile under certain combinations of critical conditions.

More particularly, the present process comprises:

(a) Polymerizing acrylonitrile, either alone or in admixture with up to about 50% in moles of at least one other copolymerizable ethylenically unsaturated monomer, using either a continuous or a semi-continuous method;

(b) Using a free-radical catalytic system having a decomposition rate constant (K greater than 1 hr. at the polymerization temperature;

(c) Using a reaction or residence time (Q) at least sufiicient to semi-decompose the catalyst; and

((1) Using a catalyst concentration (C) at least equal to 2 10- Q moles/liter, wherein Q is the reaction or residence time expressed in hours.

By semi-continuous method is intended a polymerization carried out by a continuous feed of the reactants over a definite interval of time without continuously discharging the polymerization mixture. The continuous polymerization is carried out by continuously adding the reactants to a well stirred reactor, so as to assure an homogeneous composition, and simultaneously discharging the reaction mixture over an indefinite interval of time (see Stanley Walas, Reaction Kinetics for Chemical Engineers,-Mc- Grew-Hill 1959 pages 79-100).

DESCRIPTION OF THE PREFERRED EMBODIMENTS For polymerizations carried out in stirred continuous reactors, the concentration of catalyst having a decomposition rate constant K is determined by solving the expression equating the moles fed in (C) to the sum of the reacted moles (K QC), and the moles discharged unaltered (C). The following expression is obtained: m: 1

At the semi-decomposition time (S), the following condition exists:

OI. )O=( According to Equation 1, the condition of Equation 3 is fulfilled when and inasmuch as Q S, one obtains:

Considering Equation 5 together with condition (d) above, it follows that in the case of the continuous bulk polymerization of acrylonitrile, the residence time (Q) falls within the range:

When the bulk polymerization of acrylonitrile is carried out under the foregoing conditions, the process may be easily controlled and thus becomes industrially feasible. It is noted that these conditions, i.e., the use of a catalyst having a high decomposition rate (thus a high initiation rate) and a high level of catalyst activity, are substantially different from those suggested by the prior art.

Additionally, with regard to the decomposition rate constant (K it is noted that K for a thermal catalyst is defined by the kinetic equation:

wherein (C) is the catalyst concentration in the reaction medium.

For catalytic systems of the redox type, an equation such as (7) must be completed by taking into account the concentration of the reducing agent (A) which is commonly referred to as the activator. Equation 7 thus reads:

wherein K represents the second order decomposition rate constant.

In any discussion hereinafter wherein the rate constant of a redox system is being referred to, such rate constant, although designated as K must be intended as the product K' (A), thus again reducing Equation 8 to the form of Equation 7.

If any one of the foregoing conditions (a), (b), (c), or (d) is not present, the advantages of the present process will not be realized. Thus, when the bulk polymerization of acrylonitrile is carried out with a catalytic system having a decomposition rate constant greater than 1 binin a discontinuous process, a low, industrially unacceptable conversion is obtained. This is due to the rapid decomposition of the catalytic system.

In contrast, when catalytic systems having decomposition rate constants lower than 1 hr." are used, the polymerization will be extremely sensitive to temperature. Thus, small temperature increases effect large increases in the polymerization rate, resulting in loss of control of the polymerization.

The critical effect of the decomposition rate constant of the catalyst on the temperature sensitivity of the polymerizaion is illustrated in Tables I-IV.

The data in Table I illustrate the efiect of temperature on the discontinuous polymerization rate of a mixture of monomers consisting of 83% by weight acrylonitrile and 17% by weight vinyl acetate when benzoyl peroxide, having a decomposition rate constant of 4.1 X 10- hr:- at a temperature of 55 C., is used as the catalyst. The reaction time was 60 minutes.

TABLE I Conversion rate, Concentration of Tempera percent/ catalyst (moles/liter) ture, 0. hour Similar results are observed when the catalyst was azobis-iso-butyronitrile, having a decomposition rate constant of 9.5 1(lhr:- at 50 C.

Under the same conditions used in Table I, except using a continuous polymerization procedure and azo-bisiso-butyronitrile as the catalyst, the reaction is still highly sensitive to changes in reaction temperature, as can be seen from the data in Table II:

In contrast, Table III illustrates the substantial improvement, in terms of decreased sensitivity to temperature changes, when, in accordance with the present process, a continuous polymerization procedure and a catalyst having a K; greater than 1 hr.- are used. In this case, the catalyst was a redox system consisting of cumene hydroperoxide and sodium methyl-sulfite (K =2.4 biz- The monomers reacted consisted of a mixture of 83% by weight acrylonitrile and 17% by weight vinyl acetate. The residence time was 60 minutes.

TABLE III Molar ratio sodium methyl- Concentratwnpf cumsulfite/ 'lern- Converenehydroperoxide, percumene perasion rate, cent, based on monohydroture, percent] mer mixture peroxide hr. Remarks 0.16 1 30 37.1 Polymerization medium highly fluid. 0.16 1 40 42. 6 Do. 0. 6 1 50 47. 5 D0. 0. 60 47.5 D0.

It is clear from the data in Table III that under the conditions of the present invention the temperature sensitivity of the process is minimized.

A series of continuous bulk polymerizations was carried out using a mixture of monomers consisting of 83% by weight acrylonitrile and 17% by weight vinyl acetate. The residence time was 60 minutes and the polymerization temperature 50 C. The decomposition rate constant of the catalyst (and in one case the catalyst itself) was 'varied for each polymerization. The conditions and results of this series are set forth in Table IV.

TABLE IV Con- VG!- sion Quantity rate, based on percent Catalyst (type) monomers Kd, hr=- Ihr. Remarks 1... Azo-bis-iso 2% 9.5X=- -6 Thickened rebutyronitrile. action medium:

Temperature control impossible. Cumene hydro- 0.040% Controlofthe 2 peroxile. reaction at the Sulfur dioxide 0.l69% 1. 08 12 limit of Water 60 p.p.m acceptability. Cumenedhydor- 0.040%

3 perox1 e. n fth Sulfur (llOXlde..- 0.l69% 6.1 3,525,; min Water 300 p.p.m

Cumene hydro- 0.040% Reaction medi- 4 peroxide. um very fluid.

Sulfur-dioxide--. 0.l69% 10 31 Excellent con- Water 3,000 trol ofrcaction.

p.p.m.

It should be noted that the uppermost value of K is limited (i.e. the radicals originating directly from the catalyst or catalyst components) by the combination of the. primary radical, which occurs when the product K (C) is higher than the addition rate of the primary-radicals to the monomers.

The decomposition rate constant K, of the catalyst, when it is not known, may be conveniently determined as follows:

A polymerization is carried out using a discontinuous process, i.e., feeding the monomer and .the catalytic system into the polymerizationreactor at the same time, and continuing the reaction until the maximum conversion is reached (until the complete decomposition of the catalyst is obtained). The conversion is measured at periodic time intervals during the polymerization. From this data, the time required to reach 29% of the final maximum conversion is determined. This time (s) is the semi-decomposition time of the catalyst used in a discontinuous process.

The conversion corresponding to the semi-decomposition time of thepcatalyst and the final conversion are linked by thefollowing equation 7 wherein Cs=conversion in percent corresponding, to the semi-decomposition of the catalyst in a discontinuous process; and Cf is the final conversion in percent. In discontinuous process, the semi-decomposition time s) is related to the decomposition rate constant (K by the equation:

Inasmuch as the residence time (Q) must be equal to or greater than the semi-decomposition time (S) of the cumene hydroperoxide and 0.169% by weight SO; (K =1.08 hr.- based on the monomer mixture.

TABLE V Residence Convertime (Q), Product sion, in hours KdXQ percent Remarks 1.08 12 Control of reaction temperature is at the limit of acceptability. 0.71 8.5 Control is ditlicult. 0.38 Control is impossible.

The crictical efl'ect of the catalyst concentration is illustrated by the data in Table VI. These data were obtained from the continuous bulk polymerization of a mixture consisting of 83% by weight acrylonitrile and 17% by weight vinyl acetate, at 50 C. The catalyst was cumene hydroperoxide, S0 and water. The SO /cumene hydroperoxide molar ratio was 10, and the water content of the monomer was about 0.3% by weight.

TABLE VI Concentration of the cumene hydr0- peroxide Con- Percent verbased on sion,

mon- Moles/ Q peromers liter hrs. Q 2X10- cent Remarks 0.200 13.2)(10- 1 2 10- 54.0 Reactionmedium fluid. Reaction under control.

0.160 10.5X10- 1 2X10- 49.2 Do.

5. 3X10 1 2X10 45. 8 Do. 2. 6Xl0- 1 2X10 33. 0 D0. 1.9)(10- 1 2X10" -25 Thickening of the reaction medium. Reaction out of control.

0.080 5.3X10 0.66 1.34X10 39.8 Reactionmedium fluid. Reaction under control.

0.040 2. 6X10" 0.60 1. 34X10- 28.5 D0.

0.030 1.9X10- 0.66 1.34X10 22.6 Do.

0.020 1.3X10- 0.66 1.34.}(10' x16 Thickening oi the reaction medium. Reaction out of control.

From the data in Table VI, it is apparent that the reaction mixture becomes less fluid, i.e., thickens, as the concentration of the catalyst (cumene hydroperoxide) is decreased below the value corresponding to 2.10- Q. This occurs in spite of the decreased concentration of the polymer in the reactor.

Free-radical catalysts having a high decomposition rate constant which are suitable for use in the present invention are:

organic esters including tert.butylphenylmethyl peracetate,

phenylacetyl peroxide, tert.butyl 2 (phenylthio)perbenzoate, and the like; or

catalytic systems consisting of an organic hydroperoxide ROO-H wherein R may be a linear or branched alkyl radical, a cycloalkyl or an 'aryl-alkyl-radical and an oxidizable sulfoxy compound, and a nucleophilic compound wherein, for example,

the organic hydroperoxide may be cumene-hydroperoxide,

tert.butylhydroperoxide or cyclohexanone hydroperoxide, the sulfoxy compound may be sulfur dioxide and the nucleophilic compound may be water, methyl alcohol, ethyl alcohol, or higher alcohols or an hydroxide of an alkali metal or of magnesium or of ammonium or;

an organic hydroperoxide such as, for example, cumene hydroperoxide, tert.butylhydroperoxide or cyclohexa- 7 none hydroperoxide and a mono-ester of sulfurous acid having the formula:

wherein: R and R' are the same or different, and may each be a substituted or unsubstituted linear or branched alkyl radical, or a cycloalkyl radical each of R" and R'" 7 having from 1 to 12 carbon atoms.

The preferred catalysts are those consisting of an organic hydroperoxide a nucleophilic compound and an oxidizable sulfoxy compound. Such catalysts are preferred because of their reduced cost and ease of use and handling. Moreover, the presence of the sulfoxy compound as a reducing agent provides a means for introducing sulfonic acid groups into the polymer in order to improve its dyeability with basic dyes.

In such catalytic systems, the molar ratio of the activator to the catalyst, that is, the ratio between the oxidizable sulfoxy compound and the organic hydroperoxide, is not critical insofar as the present invention is concerned. This ratio may vary Within a Wide range, e.g., from about 0.1 to 500.

Additionally, the process of the present invention is advantageous inasmuch as the slurry obtained at the reactor outlet does not require a short stopping of the polymerization and a polymer product having excellent chemical and physical properties can be easily separated from the slurry by evaporation of the volatile products therein.

It is, of course, understood that polymerization conditions (a), (b), (c) and (d) are required to be present when the process is on-line, i.e., it has reached a steady state with respect to the conversion and the catalyst concentration, but that a finite amount of time is required during he start-up to reach these conditions.

While numerous start-up procedures may be employed, we have found it preferable to use those procedures wherein the catalyst concentration is increased to the desired level as rapidly as possible. Use of an improper start-up procedure can lead to difficulty in controlling the reaction. Thus, if the catalyst and monomer are initially fed, in steady-state quantities, into a reactor fully pre-charged with the monomer, the reaction medium will suddenly thicken after -90 minutes. This leads to loss of control over the polymerization process.

The followng start-up procedure is preferred:

The catalytic system is fed into the reactor, pre-loaded to half its volume with the monomer or mixture of monomers, at the same flow rate as that of the steady state condition. 7

After a time equal to one-half of the total residence time, the monomer is fed in at the same flow rate as that of the steady state condition. Using this method, it is possible to reach the steady state concentration of the catalyst in a time corresponding to one-half the residence time, while maintaining the reaction medium in a highly fluid state.

This starting procedure may also be used for a semicontinuous process.

An alternative start-up procedure comprises pre-loading the reactor with half the volume of monomer (or mixture thereof) and then feeding the catalyst into the reactor at the same flow rate which would be used at the steady state condition. The monomer (or mixture of mon omers) is fed contemporaneously into the reactor, but at a flow rate equal to half the flow rate which would be used at the steady state condition for the entire residence time.

The polymerization may be carried out at temperatures within a wide range, the preferred temperatures being between about room temperature and 60 C. The polymerization temperature may be controlled by conventional means, e.g., immersion of the reactor in a thermostatic bath, circulating a cooling fluid around the reactor walls, internal cooling coils, or removing the reaction heat by evaporation of the reaction medium.

Preferably, the polymerization is carried out in the absence of oxygen, which has an inhibiting effect on the polymerization.

' Ethylenically unsaturated monomers" suitable for c'opolymerization with acrylonitrile in accordance with the present process include alkyl-, aryl-, and cyclo-alkylacrylates process include alkyl acrylates, aryl acrylates, and 'cycloalkyl acrylates, alkylmethacrylates, arylmethacrylates, and cycloalkyl methacrylates such as methyl; ethyl-methacrylate, isobutyl-methacrylate, and the like unsaturated ketones; vinyl esteres, such as, vinyl acetate, vinyl propionate, and the like; vinyl ethers; styrene, and its alkyl derivatives; vinyl or vinylidene chloride; vinyl fluoride; methacrylonitrile, butadiene, etc.

Additionally, the polymerization may be carried out in the presence of chain transfer agents such as the alkyl mercaptans, which also exert a fluidizing effect on the reaction, as well as in the presence of inert organic compounds such as saturated hydrocarbons, halogenated saturated hydrocarbons, and the like. The inert organic compounds exert a diluent effect on the reaction mixture.

The homopolymers and copolymers obtained using the process of the present invention possess an apparent density considerably greater than that of the polymers obtainable according to heretofore known processes. Particularly, polymers prepared with the present process always possess apparent densities greater than O.4 g./cc.

The homopolymers and copolymers prepared with the present process are suitable for transformation into fibers or filaments by conventional wet or dry spinning methods. The wet or dry spinning procedures are suitably carried out from solutions of the polymers in any of the conventionally used solvents for acrylic polymers, such as. N,N-dimethylacetamide, N,N-dimethyl formamide, ethylene carbonate, dimethyl sulfoxide, and the like, as well as in aqueous solutions of sodium thiocyanate, zinc chloride, lithium bromide, and the like.

As noted hereinabove, when the polymerization of the acrylonitrile is carried out using a sulfur compound as the reducing agent in the catalytic system, the polymers and the fibers obtained therefrom possess sulfonic acid end groups which react with basic dyes. The excellent receptivity of such polymers and copolymers of the present invention to basic dyes may be shown by determining the number of milliequivalents of ionizable sulfonic end groups available per kilogram of polymer. Numerous methods are known for making such a determination. The preferable method is that described in The Society of Dyers and Colourists, 577 (1964).

In this method, 211% by weight solution in dimethyl formamide of the polymer to be tested is prepared. This solution is then passed through an ion-exchange column containing two equal and separated quantities, respectively, of Amberlite IR (a cationic resin) in the upper part of the column, and Amberlite IR 410 (an anionic resin) in the lower part of the column. The column is 50 cm. high and has an inside diameter of 1.9 cm.

The dimethyl formamide solution, after passing through the column is then titrated for sulfonic acid groups with a methanolic solution of a quaternary ammonium base.

'9. The titration is carried out potentiometrically using a platinum electrode.

The results of the titration are expressed as milliequiva lents of sulfur, in the form of sulfonic acid groups, per kilogram of dry polymer.

It is, of course, apparent that the dyeability of the fibers obtained from this polymer is proportional to the number of milliequivalents of sulfur in the polymer as determined by this method.

The following examples further illustrate the present invention. In the examples, the intrinsic viscosity of the polymer was determined in a 0.1% dimethyl formamide solution at 25 C.

The color of the polymer was determined using a General Electric Spectrophotometer Integrator, according to the OLE. system of measurement and characterization. Under this system, the color is expressed as the purity index (PI) and brightness (B) as compared to a standard light which is an emission source corresponding to a black body heated at 6,200 K.

EXAMPLE 1 A bulk polymerization of acrylonitrile was carried out in the presence of a catalytic system consisting of cumene hydroperoxide, dimethyl sulfite and magnesium methylate. The decomposition rate constant (K of this catalytic system was determined in the following manner:

Into a 2000 cc. reactor, pre-charged with 1600 g. of acrylonitrile containing 300 p.p.m. of water and maintained at a temperature of 50 C., were added 3.2 g. of cumene hydroperoxide (0.2% by weight with respect to the monomer), 23.2 g. of dimethyl sulfite and 18.1 g. of magnesium methylate dissolved in 150 cc. of methyl alcohol. p

The polymerization started instantaneously. The polymerization course was followed by withdrawing samples every 5- minutes and measuring the conversion. The following conversion values were obtained:

Time in minutes: Conversion, percent K S=0-7 I Since s is 0.1 hour, K =7 hr.- which is within the range required for carrying out the process of the present invention, i.e., K 1 hr.-

Accordingly, the residence time (Q) of the continuous polymerization must be:

Continuous polymerization The following were continuously fed into a'2000 cc. polymerization reactor fitted with a stirrer, overflow pipe,

10 cooling system and thermometer, pre-loaded with 800 g. of acrylonitrile having a water content of 280 p.p.m., and maintained at a temperature of 50 C.:

3.2 g./hr. of cumene hydroperoxide,

23.2 g./hr. of dimethyl sulfite,

18.1 g./hr. of magnesium methylate dissolved in 150 cc.

of methyl alcohol.

After the first 30 minutes, acrylonitrile was fed into the reactor at a flow rate of 1,600 g./hr. (The total residence time was one hour.)

After about 30 additional minutes, the polymerization suspension started to discharge through the overflow pipe. The polymer collected at steadystate conditions, filtered, washed with water and dried at C. for 24 hours, amounted to 26% of the fed monomer. That is, the

' polymerization conversion amounted to 26%.

EXAMPLE 2 The following were continuously fed into a 2.5 liter polymerization reactor provided with a stirrer, cooling system, thermometer and overflow pipe, preloaded with 1000 g. of acrylonitrile having a water content of 0.3% by weight, and maintained at a temperature of 20 C.:

1.9 g./ hr. of tert.butyl hydroperoxide,

25 cc./hr. of a 10% methanol solution of sodium methyl sulfite.

Intrinsic viscosity dl./g 2.0 Monovalent sulfonic acid end groups, expressed in milliequivalents per kg. of dry polymer 26 Apparent density g./cc 0.53 Color:

PI=98.5. B=96.2.

EXAMPLE 3 The following were continuously fed into a 2.5 liter autoclave fitted with a stirrer, a thermometer and an overflow pipe, pre-loade'd to half its volume wtih a mixture consisting of 83% acrylonitrile and 17% vinyl acetate (water content=about 0.3% by weight), and maintained at a temperature of 50 C. heated at 50 C.:

. 5 g./hr. of cumene hydroperoxide;

g. /hr. of gaseous S0 The polymerization temperature of 50 C. was maintained constant by evaporation of the reaction medium and by the reflux of the condensate at atmospheric pressure.

After the first 30 minutes, the mixture of the mono: mers was continuously fed into the reactor at a flow rate of 2000 g. hr.

After 30 additional minutes, the polymeric slurry thus obtained started to discharge through the overflow pipe. At steady-state conditions, one part of this slurry, designated as (A), was filtered, washed-with Water and then dried for 24 hours at 60 C.

Another part of the slurry, designated as (B), was directly dried in an oven at C. for 5 minutes.

11 The polymerization conversion was 53% by weight. The respective polymers A and B possessed the following characteristics:

Polymer A B Intrinsic viscosity, (1 .lg 1. 5 1. 5 Monovalent sulfcnic acid end groups, expressed in milliequivalents per kg. of dry polymer 35 35 Apparent density, gJee 0. 62 0. 62 Copolymerized vinylacetate, percent 7.4 r 7. 4 Color:

PI: 98. 6 98. 6 B 95. 7 95. 8

EXAMPLE 4 The following were continuously fed into a 2000 cc. polymerization reactor fitted with a stirrer, overflow pipe, thermometer, and cooling system, pre-loaded with 800 g. of acrylonitrile having a water content of 0.30%, and maintained at a temperature of 40 C.:

4.0 g./ hr. of cumene hydroperoxide; 112 g./hr. of gaseous S After the first 30 minutes, acrylonitrile (water content of 0.3%) was fed into the reactor at a flow rate of 1,600 g./hr. The residence time was 60 minutes. After 30 additional minutes, the polymerization slurry started to discharge through the overflow pipe. The polymer was :filtered and dried at 50 C. for 6 hours.

Unless otherwise specified, the equipment, conditions and procedure were the same as those in Example 4. The reactor was pro-loaded with 800 g. of a mixture of 93% acrylonitrile and 7% methyl acrylate. (Water content of the mixture 0.3%.) The following were continuously fed into the reactor:

3.8 g./ hr. of curnene hydroperoxidc; 65 g./hr. of gaseous 80;.

After the first 30 minutes, the monomer mixture was fed into the reactor at a flow rate of 2,400 g./hr. The residence time was 40 minutes. A polyemrization conversion of 52% was obtained, and the copolymer possessed the following characteristics:

Intrinsic viscosity dl./g 2.0 Monovalent sulfonic acid groups 21 Apparent density g./cc 0.58 Copolymerized methyl acrylate percent-.. 5.3 Color:

EXAMPLE 6 The procedure of Example was followed except that the following monomer mixture was used:

96.5% acrylonitrile and 3.5% methylmethacrylate. (Water content of the mixture,

A'conversion of 47% was obtained, and the copolymer possessed the following characteristics: I

Intrinsic viscosity dl./g 2.0 Monovalent sulfonic acid groups 25 Apparent density g./cc 0.49 Copolymerized methylmethacrylate percent 4 Color:

12. EXAMPLE 7 The procedure of Example 5 was followed except that the following monomer mixture was used:

93% of acrylonitrile and 7% of methacrylonitrile. (Water content of the mixture,

A polymerization conversion of 35 was obtained, and the copolymer possessed the following characteristics:

Intrinsic viscosity dl./g Monovalent sulfonic acid groups Apparent density g./cc 0.43 Color:

EXAMPLE 8 The following were continuously fed into a 2000 cc. adiabatic polymerization reactor fitted with a stirrer, overflow pipe, and thermometer, cooled by evaporation of the reaction mass with contemporaneous condensation of the vapors by a reflux condenser maintained at 20 C. and reflux of the same into the reaction mass, and pre-loaded with 800 g. of a monomer mixture of acrylonitrile (83%) and vinylacetate (17%) (water content, 0.3%

4.0 g./ hr. of cumene hydroperoxide; g./hr. of gaseous S0 After the first 30 minutes, the monomer mixture was fed into the reactor at a flow rate of 1,650 g./hr.

The residence time was 55 minutes and the polymerization temperature was 47 C., which corresponds to the boiling temperature of the reaction mixture at room pressure.

Under such conditions, the decomposition rate of cumene hydroperoxide (CI-1P) is given by the following expression:

% =2.7 10 (CHP) moles 1. 11:

that is, a Kg value of: K =27,000 h.-

A conversion of 35% was obtained, and the copolymer possessed the following characteristics:

Intrinsic viscosity dl./g. 1.5 Monovalent sulfonic acid groups 35 Apparent density g./cc. 0.44 Copolymerized vinylacetate percent 6.5 Color:

EXAMPLE 9 The procedure of Example 5 was followed. The reactor was pre-loaded with 800 g. of a mixture consisting of 81% acrylonitrile and 19% vinylacetate maintained at a temperature of 45 C.

The following were continuously fed into the reactor:

4.4 g. hr. of cumene hydroperoxide; 5.5 g./hr. of sodium bisulphite in a 52% agueous solution; 13.5 g./hr. of gaseous S0 After the first 30 minutes, the monomer mixture was also fed into the reactor at a flow rate of 2,000 g./hr. (residence time 60 minutes).

A polymerization conversion of 48% was obtained and the copolymer possessed the following characteristics:

Intrinsic viscosity dl./g 1.5 Monovalent sulfonic acid groups 32 Apparent density g./cc 0.65 Color:

B=95.5. EXAMPLE 10 m Into a 2.5 liter autoclave fitted with a stirrer and a thermometer, pre-loadedwith 800 g. of a monomer mixture consisting of 75% acrylonitrile and 25% vinylacetate (water content of the mixture, 0.3%) and maintained at a temperature of 20 C., during one hour, the following were fed:

4 g. of cumene hydroperoxide;

24 g. of gaseous S and 800 g. of a monomer mixture consisting of 80% acrylonitrile and 20% vinylacetate.

After minutes, the temperature was raised to 40 C. and maintained at such value during the entire reaction time. After 1 hour, the feeding was stopped and the polymer was recovered by filtration of the polymerization slurry.

The polymerization conversion amounted to 35%, and the copolymer possessed the following characteristics:

Intrinsic viscosity dl./g 1.5 Monovalent sulfonic acid groups 35 Copolymerized vinylacetate percent 7 Apparent density g./cc 0.58 Color:

Variations can, of course, be made without departin from the spirit and scope of the invention.

Having thus described the invention, what is desired to be secured by Letters Patent and hereby claimed is:

1. A process for the bulk polymerization of acrylonitrile, either alone or in a mixture with up to about 50 mole percent of at least one other ethylenically unsaturated monomer copolymerizable therwith, comprising carrying out the polymerization according to a continuous or semi-continuous polymerization procedure in the presence of a free-radical catalytic system having a decomposition rate constant (K greater than 1 hr? at the polymerization temperature, the reaction or residence time in hours (Q) being at least sufiicient to semi-decompose the catalyst and QXKdZl, said catalyst being present in a concentration (C) at least equal to 2X10 Q moles/liter.

2. The process of claim 1 wherein the acrylonitrile is polymerized with another ethylenically unsaturated monomer selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, an unsaturated ketone, a vinyl ester, a vinyl ether, styrene, an alkyl derivative of styrene, vinyl or vinylidene chloride, vinyl flouride, methacrylonitrile, butadiene, and combinations thereof.

3. The process of claim 1 wherein the polymerization is carried out using a continuous method.

4. The process of claim 1 wherein the free-radical catalyst is selected from the group consisting of:

(a) an organic ester selected from the group consisting of tert.butylphenylmethyl peracetate, phenylacetyl peroxide, and tert.butyl-2-(phenylthio)perbenzoate;

(b) an organic hydroperoxide, sulfur dioxide, and a nucleophilic compound;

(c) an organic hydroperoxide and a mono-ester of sulfurous acid having the formula:

wherein R is an alkyl, cycloalkyl, aryl or alkyl-aryl radical having from 1 to 12 carbon atoms; Me is a metal of the 1st or 2nd group of the Periodic Sys- 14 tem, ammonium, or aluminum; n is 1, 2 or 3, the valency of Me; and

(d) an organic hydroperoxide, a magnesium alcoholate,

and a dialkylsulfite having the formula:

wherein: R" and R'" are the same or dilferent, and may be a substituted or unsubstituted linear or branched alkyl radical, or a cycloalkyl radical, each of R and R having from 1 to 12 carbon atoms. 5. The process of claim 1 wherein the polymerization is carried out at a temperature between about room temperature and 60 C. and in the presence of oxygen.

6. The process of claim 1 wherein the polymerization is started by:

(a) preloading a reactor to half its volume with the monomer or monomers to be polymerized;

(b) introducing the catalyst into the preloaded reactor at a flow rate equal to that which would be used at the steady-state condition of the polymerization; and

(c) after a time equal to about one half of the total reaction time, introducing the monomer or mixture of monomers into the reactor at a flow rate equal to the flow rate at the steady-state condition,

7. The process of claim 1 wherein the polymerization is started by:

(a) preloading a reactor to half its volume with the monomer or mixture of monomers to be polymerized;

(b) introducing the catalyst into the reactor at a flow rate equal to the flow rate which would be used at the steady-state condition of the polymerization; and

(c) contemporaneously with the introduction of the catalyst, introducing'the monomer or mixture of monomers into the reactor at a flow rate equal to one half the flow rate which would be used at the steady-state condition for one entire residence time.

8. The process of claim 1 wherein said acrylonitrile is polymerized alone.

References Cited UNITED STATES PATENTS 2,656,341 10/1953 DAlelio 260-881 R 2,661,363 12/1953 Dickey 260-887 D 3,635,925 1/1972 Monaco et a1. 260-855 R 3,637,622 1/1972 Monaco et al. 260-855 R 3,637,623 1/1972 Monaco et a1. 260-855 R 3,637,624 1/1972 Monaco et a1. 260-855 R 3,637,626 1/ 1972 Mazzolini et al. 260-855 R 3,637,619 1/1972 Mazzolini et a1. 260-855 R 3,637,620 1/1972 Patron et a1 260-855 R 3,637,621 1/1972 Monaco et a1. 260-855 R 3,642,737 2/ 1972 Patrone et a1. 260-855 R 3,642,738 2/ 1972 Patron et a1 260-855 R 3,644,317 2/1972 Monaco et al. 260-855 R 2,628,223 2/ 1953 Richards 260-887 R 2,654,731 10/ 1953 Patterson 260-887 R 2,745,825 5/1956 Wenning et a1. 260-887 R 3,055,877 9/1962 Singleton 260-887 R 3,525,725 8/ 1970 Kramer et a1. 260-887 R HARRY WONG, J R., Primary Examiner US. Cl. X.R.

260-29.1 R, 29.6 AN, 30.8 DS, 32.6 N, 79.3 R, 82.3, 82.5, 82.7, 83.1, 85.5 R, 85.5 P, 88.7 R, 88.7 G

PO-IOSO UNI'IED STATES PATENT OFFICE (5/69) n 1 CERTIFICATE Ob CORRECTION Patent No. 5 Dated January 21, 1974 lnventol-(s) Paolo. Melacini et al I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 9: "23 963/70" should read 23,963 A/7O Column 1, line 46: "dispersion" should read dissipation Column 2, line 17: "Onylon" should read Onyon Column 2, line. 27: "unfesible" should read unfeasible Column 3, Equation (3) (C) =2 (C) Column 4, Table II, column 2, in the heading: "Concentration, percent by Wt. should read Concentration in Z by weight with respect to the monomer Column 4, line 60: "methyl-sulfite" should read methyl sulfite Column 5, Table IV, column 2,

in the heading "Quantity based on monomers" should read Quantity based on monomers Z, Column 6, Table VI, column 4, in the heading: "Q X 2 x lO should read Q x 2 x 10 Column 6, line 67: "cumene-hydro peroxide" should read cumene hydroperoxide Column 7, line 13: "tert.butylhydroperoxide" should read tert.butyl hydroperoxide Column 7, line 49: "he" should read the Column 8, lines 21-24 should read:

-- the present process include alkyl acrylate's, aryl acrylates, and cycloalkyl acrylates such as m'ethylacrylate, ethylacrylate, isobutylacrylate and the like; .alkylmethacrylates, arylmethacrylates, and cycloalkyl methacrylates such as methyl methacrylate, Column 8,]line 26: "esteres" should read esters Column '9 line 57 .t "process From" should read process. From Column 10, line 57: "50C e heated at 50C. should read 50C. Column 1 line 49: "polyemrization" should a read polymerization Should read UNI'IED STATES PATENT OFFICE a CERTIFICATE OF CORREQTIQN Patent No. I 3, 787 365 j A Dated January 2? 1974 Inventor(s) Paolo-Melacini et 211 It is certified'that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 12, lines 38-40:

x 10 X (CHP) rooles l. h. l should read: A I r v d Elli-:1? 2,7 xl0 'x (CHP) moles 1 5. f Column 14, claim 5, line 3: "presence" should read absence a Signed and sealed this 9t day of July 1971; j

(SEAL) Attest:

McCOY M. GIBSON,JR. V C. MARSHALL DANN Attesting Officer Commissioner of Patents 

